[TTS] Add UMA histograms for IPH in CS

Add three new UMA histograms to measure: 1. The number of times Contextual Search panel is opened, categorized by whether the IPH for opening the panel was shown before. 2. The number of times Contextual Search panel is opened, categorized by whether the IPH for CS was shown before. 3. The number of times Contextual Search was triggered by tapping, categorized by whether IPH for tapping was shown before.